OS 10.5 - Os x 10.5.5

I just inherited an IBook G4, the last version, and need to update the OS to 10.5. I have a copy of 10.5.5, but the disc says its for MacBook Pro, will this still install on the iBook or do I need to get a different copy?

MacBook disc will never work. The silver grey discs are extremely model specific as you will find out. Look for a retail install DVD, black, and do not buy another silver/grey disc. Hold your breath as Leopard still fetches well over the $100 mark.

Hang on to those original install discs like grim death! Using OS X.7 or later make a bootable USB thumb drive before running Installer!

There's no such thing as an OS X disc that is "named" Universal Binary.
According to my memory, you'll not find anything on the disc or the original box that says "universal binary".

There are the retail copies (black) and there are the copies that shipped with individual computers (grey). There are also drop in copies of upgrade discs for Leopard (these are black also) that were provided with Macs that shipped with Tiger after Leopard was released. These require that 10.4 already be installed.

A disc (the grey ones) that shipped with an individual computer will only work on other "same model" Macs. So one that says it is for a MBP, will not work on your G4. Or for that matter, on any model Mac except the same model MBP with which it shipped.

One of those 'drop in' discs - it won't work on your G4 either - not only do they require you to have 10.4 installed on the machine, but they are all Intel only as well. I do not know if these drop in discs are model specific or not.

You will need a black retail copy of Leopard (which incidentally, would be a universal binary and can be installed on both PPC and Intel Macs) to install it onto your G4.

The retail disc will be in a box that looks like this:

Those drop in discs, they shipped in a plain black wrapping. So make sure you get one like the above.

I cannot be held responsible for the things that come out of my mouth.
In the Windows world, most everything folks don't understand is called a virus.

No. You can try calling Apple customer support and see if they're still selling Leopard but I'm betting they're no longer available. Like Harry advised above you probably will need to find a copy on eBay - and also like he said, it will be expensive.